Electronic battery tester with tailored compensation for low state-of charge

ABSTRACT

Various embodiments of an improved electronic device for testing or monitoring storage batteries that may be only partially charged are disclosed. The device determines the battery&#39;s small-signal dynamic conductance in order to provide either a proportional numerical readout, displayed in appropriate battery measuring units, or a corresponding qualitative assessment of the battery&#39;s relative condition based upon its dynamic conductance and electrical rating. The device also determines the battery&#39;s terminal voltage in an essentially unloaded condition and utilizes this information to automatically correct the measured dynamic conductance. The automatic correction is performed by the electronic device using information or functions which are tailored for the particular type of battery being tested. By virtue of this automatic correction, the quantitative or qualitative information displayed to the user conforms with that of a fully-charged battery even though the battery may, in actual fact, be only partially charged. If the battery&#39;s state-of-charge is too low for an accurate assessment to be made, no information is displayed. Instead, an indication is made to the user that the battery must be recharged before testing.

BACKGROUND OF THE INVENTION

This application is a Continuation-In-Part of patent applicationentitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOWSTATE-OF-CHARGE, United States patent application Ser. No. 08/496,467,filed Jun. 29, 1995, now U.S. Pat. No. 5,585,728, which is a filewrapper continuation of Ser. No. 08/292,925, filed on Aug. 18, 1994, nowabandoned, which is a file wrapper continuation of Ser. No. 07/877,646,filed May 1, 1992, now abandoned.

This invention relates to an electronic measuring or monitoring devicefor assessing the ability of a storage battery to deliver power to aLoad. More specifically, it relates to improved apparatus of the typedisclosed previously in U.S. Pat. Nos. 3,873,911, 3,909,708, 4,816,768,4,825,170, 4,881,038, and 4,912,416 issued to Keith S. Champlin.

Storage batteries are employed in many applications requiring electricalenergy to be retained for later use. Most commonly, they are employed inmotor vehicles utilizing internal combustion engines. In suchapplications, energy stored by "charging" the battery during engineoperation is later used to power lights, radio, and other electricalapparatus when the engine is stopped. The most severe demand upon thebattery of a motor vehicle is usually made by the starter motor. Failureto supply the starter motor with sufficient power to crank the engine,particularly in cold weather, is often the first indication of batterydeterioration. Clearly, a simple measurement that accurately assesses abattery's ability to supply cranking power is of considerable value.

Prior to the introduction of the dynamic conductance testing methoddisclosed in the six U.S. patents enumerated above, the method mostgenerally available for assessing a battery's ability to supply crankingpower was the standard load test. This test subjects a battery to aheavy dc current having a predetermined value dictated by the battery'srating. After a prescribed time interval, the battery's voltage underload is observed. The battery is then considered to have "passed" or"failed" the load test according to whether its voltage under load isgreater, or less, than a particular value.

Although the standard load test has been widely used for many years, ithas several serious disadvantages. These include:

1. The test draws a large current and therefore requires apparatus thatis heavy and cumbersome.

2. Considerable "sparking" can occur if the test apparatus is connectedor disconnected under load conditions. Such "sparking" in the presenceof battery gasses can cause an explosion with the potential for seriousinjury to the user.

3. A standard load test leaves the battery in a significantly reducedstate-of-charge and therefore less capable of cranking the engine thanbefore the test was performed.

4. The battery's terminal voltage decreases with time during performanceof the load test. Accordingly, test results are generally imprecise andoften dependent upon the skill of the operator.

5. Load test results are not repeatable since the test itselftemporarily polarizes the battery. Such test-induced polarizationsignificantly alters the initial conditions of anysubsequently-performed tests.

A practical alternative to the standard load test is taught in the sixU.S. Patents enumerated above. These documents disclose electronicapparatus for accurately assessing a battery's condition by means ofsmall-signal ac measurements of its dynamic conductance. They teach thata battery's dynamic conductance is directly proportional to its dynamicpower--the maximum power that the battery can deliver to a load. Dynamicconductance is therefore a direct measure of a battery's ability tosupply cranking power.

In comparison with the load test method of battery appraisal, thedynamic conductance testing method has many advantages. For example,dynamic conductance testing utilizes electronic apparatus that is smalland lightweight, draws very little current, produces virtually nosparking when connected or disconnected, does not significantlydischarge or polarize the battery, and yields accurate, highlyreproducible, test results. Virtually millions of battery measurementsperformed over the years have fully corroborated these teachings andhave proven the validity of this alternative testing method.

One disadvantage, however, of the dynamic conductance testing method hasbeen the fact that test results are somewhat dependent upon thebattery's state-of-charge. Accordingly, the methods and apparatusdisclosed in the first five of the six U.S. patents cited above havegenerally required that the battery be essentially fully charged to betested. Since many batteries are, in fact, fairly discharged when theyare returned for replacement under warranty, or when they are otherwisesuspected of being faulty, it has been frequently necessary to rechargea battery before testing it. Such recharging is costly andtime-consuming. Clearly, a simple method for performing accurate dynamicconductance tests on batteries "as is"--batteries that may be onlypartially charged--would be of considerable benefit.

Great progress toward solving this problem has been engendered by themethods and apparatus disclosed in the sixth U.S. patent cited above;U.S. Pat. No. 4,912,416. As is well known to those skilled in the art, abattery's state-of-charge is directly related to its open-circuit(unloaded) terminal voltage. By utilizing this fact, along withextensive experimental data, an empirical relationship was establishedbetween a battery's state-of charge, as reflected by its open-circuitvoltage, and its relative dynamic conductance, normalized with respectto its fully-charged value. This empirical relationship was firstdisclosed in U.S. Pat. No. 4,912,416. Further, apparatus disclosedtherein utilized this empirical relationship, along with measurements ofopen-circuit voltage, to appropriately correct dynamic conductancereadings--thus yielding battery assessments that were essentiallyindependent of the battery's state-of-charge.

However, the measuring apparatus disclosed in U.S. Pat. No. 4,912,416utilized an inconvenient two-step testing procedure requiringintermediate interaction by the user. The battery's open-circuit voltagewas first measured. Next, using the results of the voltage measurement,the user adjusted a variable attenuator to an appropriate setting.Finally, the dynamic conductance was measured. By virtue of thepreviously adjusted variable attenuator, the quantitative or qualitativedynamic conductance information ultimately displayed to the userconformed with that of a fully-charged battery even though the batterymay, in actual fact, have been only partially charged when tested. Thestate-of-charge problem was thus solved in principle by the methods andapparatus taught in U.S. Pat. No. 4,912,416.

Measuring apparatuses and methods which compensate a battery's relativeconductance based upon the teaching of U.S. Pat. No. 4,912,416 workextremely well for "standard" (i.e., "acid-limited") batterytypes--batteries for which the relationship between the state-of-chargeand the relative dynamic conductance closely follows the empiricalrelationship disclosed in U.S. Pat. No. 4,912,416. However, this"standard" empirical relationship does not work as well for compensatingthe relative dynamic conductance of batteries constructed differently,for which the "standard" empirical relationship may not be as accurate.For example, a battery designed for use in warmer climates may have alower plate count for its size as compared to a more expensive batterywhich has more plates per acid volume. The higher plate count battery("acid-starved") will typically provide power down to a much lowervoltage than will the lower plate count ("acid-flooded") battery. Thus,a "standard" charge compensation curve will tend to overcompensate thebattery with the high plate count and undercompensate the battery withthe low plate count.

It is therefore quite apparent that an improved apparatus which providesautomatic state-of-charge correction for a wide variety of battery typeswould be highly advantageous. Just such an improved electronic batterytesting apparatus, providing for automatic correction for lowstate-of-charge for a wide variety of battery types, is disclosed hereinbelow.

SUMMARY OF THE INVENTION

Various embodiments of an improved electronic device for testing ormonitoring storage batteries that may be only partially charged aredisclosed. The device determines the battery's small-signal dynamicconductance in order to provide either a proportional numerical readout,displayed in appropriate battery measuring units, or a correspondingqualitative assessment of the battery's relative condition based uponits dynamic conductance and electrical rating. The device alsodetermines the battery's terminal voltage in an essentially unloadedcondition and utilizes this information to automatically correct themeasured dynamic conductance. The automatic correction is performed bythe electronic device using information or functions which are tailoredfor the particular type of battery being tested. By virtue of thisautomatic correction, the quantitative or qualitative informationdisplayed to the user conforms with that of a fully-charged battery eventhough the battery may, in actual fact, be only partially charged. Ifthe battery's state-of-charge is too low for an accurate assessment tobe made, no information is displayed. Instead, an indication is made tothe user that the battery must be recharged before testing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the Thevenin's equivalent circuit of a lead-acid storagebattery comprising its open-circuit voltage, V_(o), and its internalresistance, R_(x), connected in series.

FIG. 2 is an empirical plot of normalized dynamic conductance, G_(x),versus open-circuit voltage, V_(o), showing the correlation withmeasurements performed upon four different "standard" (acid-limited)lead-acid storage batteries having differing electrical ratings andfabricated by different manufacturers.

FIG. 3 is a simplified block diagram of an improved electronic batterytesting/monitoring device employing automatic compensation for lowstate-of-charge in accordance with a first embodiment of the presentinvention.

FIG. 4 is a graphical plot of the state-of-charge correction factorobtained by taking the reciprocal of the "standard" empirical normalizeddynamic conductance curve of FIG. 2.

FIG. 5 is a plot of a four-segment piecewise-linear approximation to thecorrection factor curve of FIG. 4 implemented by the correctionamplifier circuit disclosed in FIG. 6.

FIG. 6 is a schematic diagram of a dc correction amplifier embodimentwhich implements the four-segment piecewise-linear transfer functiondisclosed in FIG. 5.

FIG. 7 is a complete schematic diagram of an improved electronic batterytesting/monitoring device with automatic compensation for lowstate-of-charge configured for testing/monitoring "standard" 12-voltautomotive batteries.

FIG. 8 is a graphical plot similar to FIG. 4 but illustratingstate-of-charge correction factors for five different types ofbatteries.

FIG. 9 is a simplified block diagram of an embodiment of an improvedelectronic battery testing/monitoring device which provides battery typespecific automatic compensation for low state-of-charge.

FIG. 10 is a simplified block diagram of another embodiment of animproved electronic battery testing/monitoring device which providesbattery type specific automatic compensation for low state-of-charge.

FIG. 11 is a simplified block diagram illustrating one embodiment of thecorrection amplifier of the device shown in FIG. 3 which can be used toimplement the multiple charge compensation curve approach of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the Thevenin's equivalent circuit of alead-acid storage battery is shown. In this equivalent representation,the battery is described by its open-circuit voltage, V_(o), and itsinternal resistance, R_(x), connected in series.

As has been fully disclosed in the first five of the six U. S. Patentscited above, a conventional dynamic conductance battery test of afully-charged battery traditionally ignores the open-circuit voltage,V_(o). Instead, the electronic test apparatus directly measures thebattery's dynamic conductance G_(x) =1/R_(x). The testing/monitoringdevice then provides the operator with either a numerical readoutdisplayed in proportional battery measuring units (such as "ColdCranking Amps", "Ampere-Hours", or "Watts") or else with a qualitativedisplay ("Pass/Fail") based upon comparing the measured value of G_(x)with a corresponding reference value determined from the battery'selectrical rating and temperature.

Although the open-circuit voltage, V_(o), has not been normally used indynamic conductance testing of fully-charged batteries, it has beenpreviously used to determine state-of-charge. As is well known to thoseskilled in the art, a battery's state-of-charge is directly related toits open-circuit (unloaded) terminal voltage. For example, with"standard" (acid-limited) automotive-type lead-acid batteries havingnominal voltage of 12 volts, the open-circuit voltage is known to varyfrom about 11.4 volts, for batteries that are virtually totallydischarged, to about 12.6 volts, for batteries that are nearly fullycharged.

FIG. 2 shows the observed relationship between normalized dynamicconductance and open-circuit voltage appropriate to "standard"(acid-limited) automotive-type lead-acid storage batteries. Thisinformation was disclosed previously in U. S. Pat. No. 4,912,416. FIG. 2displays an empirical graph of relative dynamic conductance, normalizedwith respect to the fully-charged value, G_(x) (V_(o))/G_(x) (12.6),plotted as a function of open-circuit voltage, V_(o). The solid curveplotted in FIG. 2 is described by a second-order polynomial equationhaving coefficients adjusted to best fit the experimental data. Theappropriately adjusted polynomial equation is: ##EQU1##

FIG. 2 also discloses normalized experimental points which representactual measurements obtained from four different "standard"-type(acid-limited) batteries possessing different electrical ratings andfabricated by different manufacturers. Batteries XM0, XM1, and XM3 aresix-cell batteries having nominal voltages of 12 volts. Battery XM2 isactually a three-cell, 6-volt battery. Open-circuit voltage measurementsof battery XM2 were multiplied by a factor of two in order to plot XM2data points on the same graph as the other three batteries. One seesthat the normalized measurements obtained from all four batteries agreequite closely with the empirical relation described by Equation (1). Thefact that the same empirical relation shows strong correlation withexperimental data obtained from both 6-volt and 12-volt batteriesindicates that the empirical state-of-charge correction disclosed inFIG. 2 is quite universal and is actually a fundamental property of asingle cell.

Referring now to FIG. 3, a simplified block diagram of a firstembodiment of an improved electronic battery testing/monitoring devicewith automatic compensation for low state-of-charge is disclosed. Exceptfor specific details having to do with the circuitry for automaticcompensation for low state-of-charge, the explanation of the operationof the block diagram of FIG. 3 is identical with that of thecorresponding block diagram referred to as FIG. 1 in U.S. Pat. No.4,816,768.

Accordingly, signals representative of the signal at output 10 ofhigh-gain amplifier cascade 12 are fed back to input 20 of high-gainamplifier cascade 12 by means of two feedback paths; internal feedbackpath 14 and external feedback path 16. Internal feedback path 14includes low pass filter (LPF) 18 and feeds a signal directly back toinput 20 of high-gain amplifier cascade 12. The purpose of internalfeedback path 14 and low pass filter 18 is to provide large dc feedbackbut relatively little ac feedback in order to define the operating pointof high-gain amplifier cascade 12 and ensure its dc stability withoutappreciably reducing its ac voltage gain. External feedback path 16contains resistive network 22 and feeds a signal current back to thebattery undergoing test 24. Summation circuitry 26 combines theresulting signal voltage 28 developed thereby across battery 24 with a100 Hz periodic square-wave signal voltage 30.

In the embodiment disclosed in FIG. 3, the periodic square-wave signalvoltage 30 is formed by the action oscillator 32, chopper switch 34, anddc correction amplifier (Cor Amp) 36. The oscillation frequency ofoscillator 32 may, for example, be 100 Hz. The voltage applied to input38 of dc correction amplifier 36 is the dc terminal voltage of battery24. By virtue of the fact that the electronic apparatus disclosed inFIG. 3 draws very little load current from the battery, this terminalvoltage is essentially the battery's open-circuit (unloaded) terminalvoltage V_(o). Signal output 40 of dc correction amplifier 36 is a dcvoltage derived from V_(o) --having a voltage level that is inverselyrelated to V_(o) --and hence inversely related to the state-of-charge ofbattery 24. This derived dc voltage 40 is repetitively interrupted bychopping switch 34 whose control input 42 is activated by the output ofoscillator 32. The chopped dc voltage thus comprises a periodicsquare-wave signal voltage 30 having a voltage amplitude chat isinversely related to V_(o), and hence inversely related to thestate-of-charge of battery 24. This signal voltage 30 is presented tosummation circuitry 26 along with the signal voltage 28 developed acrossbattery 24. The resulting composite signal voltage 44 at the output ofsummation circuitry 26 is then capacitively coupled to input 20 ofhigh-gain amplifier cascade 12 by means of capacitive coupling network46.

As has been fully explained in U.S. Pat. No. 4,816,768, the voltage atout-put 10 of high-gain amplifier cascade 12 comprises a constant dcbias component along with an ac signal component that is proportional tothe dynamic conductance G_(x) of the battery undergoing test 24 as wellas to the level of the square-wave signal voltage 30. The constant dcbias component is ignored while the variable ac signal component isdetected and accurately converted to a dc signal voltage by synchronousdetector 48, synchronized to oscillator 32 by means of synchronizingpath 50.

The dc signal voltage at output 52 of synchronous detector 48 passesthrough adjustable resistive network 54 to the input of dc-coupledoperational amplifier 56. Feedback path 58 of operational amplifier 56contains dc milliammeter 60. Accordingly, the reading of dc milliammeter60 is proportional to the dc signal voltage level at the output 52 ofsynchronous detector 48, and hence to the dynamic conductance G_(x) ofbattery 24. In addition, the constant of proportionality relating themilliammeter reading to G_(x) is determined by the value assumed byadjustable resistive network 54 as well as by the level of the signalvoltage at 30--and hence by the battery's state-of-charge as exemplifiedby its unloaded dc terminal voltage V_(o).

By utilizing an appropriate fixed resistance value in resistive network54 and then calibrating milliammeter 60 in battery measuring unitnumbers that are proportional to the battery's dynamic conductance, theembodiment disclosed in FIG. 3 will emulate the direct reading batterytester disclosed in U.S. Pat. 3,873,911. In addition, as is fully taughtin U.S. Pat. No. 4,816,768, the resistance value of resistive network 54which brings the reading of dc milliammeter 60 to a particular fixedvalue is directly proportional to the dynamic conductance of battery 24.Hence, by calibrating resistive network 54 in traditional battery ratingunits, and then designating "pass" and "fail" regions on the face ofmilliammeter 60, the embodiment disclosed in FIG. 3 will also emulatethe "pass-fail" battery testing device disclosed in U.S. Pat. No.3,909,708. Furthermore, one can employ a switch to select either afixed-valued resistive network 54 or an adjustable-valued network 54 andcan arrange both a number scale and "pass-fail" regions on the face ofmilliammeter 60. One can therefore realize both a direct-reading batterytester and a "pass-fail" battery tester with a single device.

For either emulation, the amplitude of the detected signal at the output52 of synchronous detector 48 is directly proportional to the amplitudeof the square-wave signal 30 at the output of chopper switch 34. Hence,both the level of the numerical quantity displayed during direct-readingoperation as well as the relative qualitative assessment provided in"pass-fail" operation are influenced by the battery's "state-of-charge",as exemplified by its unloaded terminal voltage V_(o). In order for thisdisplayed information to be independent of the battery'sstate-of-charge, one must require V_(out), the dc output voltage at 40of dc correction amplifier 36, to be proportional to the reciprocal ofG_(x) (V_(o)). Under these conditions, V_(out) can be written as:

    V.sub.out (V.sub.o)-V.sub.out (12.6)×F(V.sub.o)      Eq. 2

where: ##EQU2## is an appropriate state-of-charge "correction factor"imposed by correction amplifier 36. Rearranging Equation 2 leads to:##EQU3## which shows that F(V_(o)) may be simply regarded as the dcoutput voltage of amplifier 36 normalized with respect to thecorresponding dc output voltage obtained with a fully-charged battery;i.e., a battery for which V_(o) =12.6 volts.

In addition to providing a dc signal output 40, the dc correctionamplifier 36 also provides a "Chopper Disable" output 62 and an LEDoutput 64. These two additional outputs become activated whenever thebattery's terminal voltage V_(o), and hence its state-of-charge, is toosmall for an accurate dynamic conductance test to be made. Under thesespecial conditions, chopper switch 34 becomes disabled so that noqualitative or quantitative information is displayed to the user.Instead, LED 66 lights to indicate to the user that the battery must berecharged before it can be tested.

FIG. 4 displays a graphical plot of the state-of-charge correctionfactor F(V_(o)) obtained by taking the reciprocal of the empirical{G_(x) (V_(o))/G_(x) (12.6)} curve disclosed in FIG. 2. A four-segmentpiecewise-linear approximation to this empirical curve is disclosed inFIG. 5. The parameters which specify the four breakpoints of thispiecewise-linear approximation are listed in Table I.

                  TABLE I                                                         ______________________________________                                        Piecewise-Linear Approximation Parameters                                     Breakpoint   V.sub.o (Volts)                                                                        Correction Factor - F                                   ______________________________________                                        A            12.60    1.00                                                    B            12.15    1.21                                                    C            11.80    1.78                                                    D            11.60    2.91                                                    ______________________________________                                    

The piecewise-linear input-output relationship of FIG. 5 is implementedby the transfer function of the dc correction amplifier circuitembodiment disclosed in FIG. 6. Referring now to FIG. 6, the dccorrection amplifier contained generally in block 36 comprises theinterconnection of four operational amplifiers, 70, 72, 74, and 76 alongwith comparator 78. Circuit input lead 38 connects to the positiveterminal of the battery 24 under test, while the negative batteryterminal is grounded. By virtue of the fact that very little current isdrawn from battery 24, the circuit's input voltage at 38, V_(in),measured with respect to ground, is essentially equal to the battery'sopen-circuit terminal voltage V_(o).

Within the dc correction amplifier circuit disclosed in FIG. 6, aconstant reference voltage V_(R) is established by means of voltagereference diode 80 receiving operating current through series resistor82. Reference voltage V_(R) may, for example, be 2.5 volts. V_(R) isfurther operated on by a voltage divider chain comprising resistors 84,86, 88, and 90. Accordingly, the voltage level applied to thenoninverting inputs of operational amplifiers 70 and 72 is V_(R), whileincreasingly smaller fractions of reference voltage V_(R) are applied tothe noninverting inputs of operational amplifiers 74 and 76 and to theinverting input of comparator 78, respectively. In addition to thesefixed voltage levels, a variable voltage V_(x), that is proportional tobattery voltage V_(o), is derived from V_(in) by means of voltagedivider resistors 92 and 94. This variable voltage is applied directlyto the noninverting input of comparator 78 and to the inverting inputsof operational amplifiers 72, 74, and 76 through resistors 98, 102, and106, respectively.

The outputs of the four operational amplifiers, 70, 72, 74, and 76, areconnected to a common output bus, V_(out), through the four diodes, 108,110, 112, and 114, respectively. Because of the operation of these fourdiodes, only one of the operational amplifiers will be active at any onegiven time--the amplifier having the largest (most positive) outputvoltage. That operational amplifier alone will be connected to theoutput bus and will thus be controlling the output voltage V_(out). Theother three operational amplifiers, those having smaller outputvoltages, will be disconnected from the output bus by virtue of theirhaving reverse-biased diodes in their output circuits.

Operational amplifier 70 has its inverting input connected directly tothe output bus and is therefore configured as a unity-gainvoltage-follower amplifying the reference voltage V_(R). Operationalamplifiers 72, 74, and 76 utilize feedback resistors and are configuredas inverting amplifiers; each amplifying the variable voltage V_(x) ;and each providing a negative incremental voltage gain given,respectively, by the appropriate resistance ratio {R(96)/R(98)},{R(100)/R(102)}, or {R(104)/R(106)}.

The circuit of FIG. 6 functions as follows: For V_(in) >V_(A) =12.6volts, the output voltage of operational amplifier 70 will be largerthan the output voltages of the other three operational amplifiers.Accordingly, the output bus will be controlled by the unity-gainvoltage-follower amplifier 70 so that V_(out) =V_(R). This region ofconstant output-voltage is represented by segment 1 in thepiecewise-linear transfer function displayed in FIG. 5.

When V_(in) has decreased to V_(A) =12.6 volts, V_(x) will have becomesufficiently less than V_(R) that the output of inverting amplifier 72will equal that of amplifier 70. Thus, for V_(in) <V_(A), diode 108 willbe reverse biased while diode 110 will be forward biased, and amplifier72 will control the output bus. Due to the amplification of invertingamplifier 72, further decreases in V_(in) will cause V_(out) to increasewith incremental gain or "slope" of -{(R96)/R(98)}. This region ofamplification, which continues unitil V_(in) =V_(B), is represented bysegment 2 in FIG. 5.

When V_(in) has decreased to V_(B), V_(X) will have decreasedsufficiently that the output of inverting amplifier 74 will exceed thatof amplifier 72. Diode 110 will therefore be reverse biased while diode112 will be forward biased, and amplifier 74 will now control the outputbus. Due to the amplification of inverting amplifier 74, furtherdecreases in V_(in) will cause V_(out) to increase with the largerincremental gain or "slope" of -{R(100)/R(102)}. This region ofamplification continues until V_(in) =V_(c) and is represented bysegment 3 in FIG. 5.

When V_(in) has decreased to V_(c), V_(x) will have decreasedsufficiently that the output of inverting amplifier 76 will exceed thatof amplifier 74. Diode 112 will therefore be reverse biased while diode114 will be forward biased. Thus, amplifier 76 will now control theoutput bus. Due to the amplifying action of inverting amplifier 76, anyfurther decreases in V_(in) will cause V_(out) to increase with thestill larger incremental gain or "slope" -{R(104)/R(106)}. This regionof largest amplification is represented by segment 4 in FIG. 5.

Finally, for V_(in) <V_(D), the derived voltage V_(x) will be less thanthe tapped-down reference voltage existing at the point ofinterconnection of resistors 88 and 90. Under these special conditions,the noninverting input of comparator 78 will be at a lower potentialthan the inverting input thus causing comparator 78's output to be in a"low" state. As a consequence, LED 66 will be lit to provide anindication to the user that the battery must be recharged before it canbe tested. In addition, output line 62 will be in a "low" state, thusdisabling chopper switch 34 and preventing any qualitative orquantitative dynamic conductance information from being conveyed to theuser.

FIG. 7 discloses a complete schematic diagram of a first embodiment ofan improved electronic battery testing/monitoring device with automaticstate-of-charge compensation configured or testing/monitoring 12-voltbatteries in accordance with the present invention. Operationalamplifiers 120, 122, 124, and 126 comprise four elements of a quadoperational amplifier integrated circuit, ICI. Bilateral analog switches34 and 128 comprise two elements of a quad CMOS bilateral switchintegrated circuit, IC2. Operational amplifiers 70, 72, 74, and 76comprise four elements of a quad operational amplifier integratedcircuit, IC3. Comparator 78 comprises one element of a quad comparatorintegrated circuit IC4. All four integrated circuits, ICl, IC2, IC3, andIC4 are powered by means of common power connections, V⁺ 130 and V⁻ 132,connected to the battery undergoing test 24 through battery contacts 134and 136, respectively.

High-gain amplifier cascade 12 of FIG. 3 comprises operational amplifier120 and npn transistor 138 connected as an emitter follower. Resistor140 conducts a dc bias voltage to the noninverting (+) input ofoperational amplifier 120 from voltage divider resistors 142 and 144which are connected to battery 24 through battery contacts 146 and 148.The output voltage of high-gain amplifier cascade 12 is establishedacross external-path feedback resistor 22. An internal feedback pathcomprising resistors 150 and 152 conducts the dc voltage at the commonconnection between the emitter of npn transistor 138 and resistor 22 tothe inverting (-) input of operational amplifier 120. Resistors 150 and152 along with capacitor 154 comprise low-pass filter 18 of FIG. 3.

The ac signal voltage developed across battery 24 is sensed at batterycontacts 146 and 148 and added in series to an input signal voltagecomponent established across viewing resistor 156. The resultantcomposite ac signal voltage is coupled to the differential input ofoperational amplifier 120 by means of a capacitive coupling networkcomprising capacitors 158 and 160. A feedback current that isproportional to the voltage established across resistor 22 passesthrough battery 24 by means of external feedback path conductors 162 and164 along with battery contacts 134 and 136.

An ac square-wave input signal voltage is established across viewingresistor 156 and is formed by the action of oscillator 32, chopperswitch 34, and correction amplifier 36. Oscillator 32, which generates a100 Hz square-wave synchronizing signal, is a conventional a stablemultivibrator comprising operational amplifier 122 along with resistors168, 170, 172, 174, and capacitor 176. The synchronizing output signalof oscillator 32 is conducted to the control input of chopper switch 34through resistor 178. Accordingly, chopper switch 34 turns on and offperiodically at a 100 Hz rate. The signal terminals of chopper switch118 interconnect the dc signal output 40 of correction amplifier 36 withthe input lead of trimmer potentiometer 180 used for initial calibrationadjustment. The signal voltage across trimmer potentiometer 180therefore comprises a 100 Hz square wave having amplitude proportionalto the dc output voltage of correction amplifier 36. A signal currentproportional to the signal output voltage of trimmer potentiometer 180passes through injection resistor 184 and is injected into viewingresistor 156 thereby developing a 100 Hz signal voltage across viewingresistor 156.

By virtue of the action of correction amplifier 36 described withreference to FIG. 6, the signal voltage across viewing resistor 156 willcontain an automatic correction for the state-of-charge of the batteryundergoing test. If, however, the battery's state-of-charge is too lowfor an accurate battery assessment to be made, the correctionamplifier's output lines 62 and 64 will be in logic low states. Theseoutput lines will, in turn, pull the control input of chopper switch 34low and pull the cathode of LED 66 low. As a result, chopper switch 34will be disabled so that no ac signal will be injected into viewingresistor 156, and LED 66 will light to indicate to the user that thebattery must be recharged before a dynamic conductance test can beperformed.

Analog switch 128 along with operational amplifier 124, which isconnected as an integrator, comprise synchronous detector 48 of FIG. 3.Resistor 194 and bypass capacitor 196 comprise a low-pass filter whichbiases the noninverting input of operational amplifier 124 to thevoltage level of the dc bias component developed across feedbackresistor 22. A signal current derived from the total voltage at thecommon connection between resistor 22 and transistor 138 passes throughresistor 198 and analog switch 128 to the inverting input of operationalamplifier 124. This signal current is periodically interrupted at theoscillator frequency by virtue of the control input of analog switch 128being connected to the synchronizing output of oscillator 32. Resistor200 provides negative dc feedback to operational amplifier 124.Integration capacitor 202 serves to smooth the detected voltage signaloutputted by operational amplifier 124.

The noninverting input of operational amplifier 126 is biased to the dclevel of the noninverting input of operational amplifier 124 while theinverting input of operational amplifier 126 is connected to SPDTselector switch 206. Accordingly, a dc current proportional to thedetected signal voltage at the output of operational amplifier 124passes through milliammeter 60 to the output of operational amplifier116 by way of one of the two paths selected by selector switch 206. Withswitch 206 in position 1, the meter current passes through fixedresistor 208. Under these conditions, the disclosed invention emulates adirect reading battery testing device providing a quantitative outputdisplayed in battery measuring units that are proportional to thedynamic conductance of battery 24. With switch 206 in position 2, themeter current passes through fixed resistor 210 and variable resistor212. Under these conditions the disclosed invention emulates aqualitative, "pass-fail", battery testing device having a manuallyadjusted battery rating scale that is linearly related to the setting ofvariable resistance 212, and a rating offset that is determined by thevalue of fixed resistor 210.

The improved battery testing/monitoring device embodiment havingautomatic compensation for low state-of-charge disclosed in FIG. 7 isoperated as follows: The operator simply connects the device to thebattery undergoing test and selects one of the two positions of selectorswitch 206. If position 1 is selected, meter 60 will display thebattery's quantitative condition in appropriate battery measuringunits--with the displayed quantitative results having been automaticallyadjusted to conform with those of a fully-charged battery. If switch 206is in position 2, and variable resistance 212 has been set in accordancewith the battery's rating, meter 60 will display the battery'squalitative ("pass/fail") condition. Again, the displayed results willhave been automatically adjusted to conform with those of afully-charged battery. With either selection, if the battery'sstate-of-charge is too low for an accurate assessment to be made, noinformation will be displayed to the user. Instead, an LED will light toindicate to the user that the battery must be recharged before testing.

Table II contains a listing of component types and values for the firstembodiment of an improved electronic battery testing/monitoring devicewith automatic compensation for low state-of-charge disclosed in FIG. 7.

                  TABLE II                                                        ______________________________________                                        Component Types and Values for Circuit of FIG. 7                              REFERENCE NUMBER     COMPONENT                                                ______________________________________                                        Semiconductor Devices                                                         120, 122, 124, 126   IC1 - LM324N                                             34, 128              IC2 - CD4066B                                            70, 72, 74, 76       IC3 - LM324N                                             78                   IC4 - LM339                                              80                   IC5 - LM336-2.5                                          138                  TIP31C Power                                                                  Transistor                                               108, 110, 112, 114   1N4148 Diodes                                            66                   T-1 3/4 LED                                              Resistors - Ohms (1/4-W unless specified)                                     5 Watts              22Ω                                                82                   4.7K                                                     84                   5.36K                                                    86                   6.19K                                                    88                   6.04K                                                    90                   200K                                                     92                   2.25K                                                    94                   576                                                      96, 100, 104         1.00M                                                    98                   174K                                                     102                  49.9K                                                    106                  13.7K                                                    116, 142, 144        1.0K                                                     156, 210             100                                                      208                  470                                                      212                  500 Variable                                             180                  10K Trimpot                                              184                  470K                                                     140, 200             47K                                                      178, 194, 198        100K                                                     172                  150K                                                     174                  270K                                                     150, 152, 168, 170   1 Meg                                                    Capacitors - Mfd                                                              176                  0.022                                                    154, 158, 160, 196   0.47                                                     202                  1.0                                                      Meter                                                                         204                  1 mA dc milliammeter                                     Switch                                                                        206                  SPDT                                                     ______________________________________                                    

Frequently, modern batteries are designed for specific cost targets andspecific applications. For example, a low cost battery which may be usedin warmer climates may have a lower plate count (less active materialsurface area) for its size as compared to a colder climate battery whichcosts more and has a higher plate count (more plates per acid volume).The low plate count battery may consume all plate surface area by thetime the battery discharges to a voltage of only about 12.4 volts, whilethe battery with a relatively higher plate count will be able to providepower at much lower voltages. A wide variety of different battery typesare available, using different technologies and construction techniques.The various battery types have different relationships between thebattery's open circuit voltage and its relative dynamic conductance.Therefore, using a single "standard" state-of-charge correction factorcurve for all battery types can tend to overcompensate some batteries,while undercompensating other batteries.

In order to improve the accuracy of the state-of-charge correction ofthe present invention, a potentially infinite number of differentstate-of-charge correction factor curves, corresponding to differentbattery types, can be used. Like the single correction factor curveapproach, the multiple correction factor curve approach of the presentinvention uses empirical data to establish the correction factor curvesin the manner described above. From a practical standpoint, it has beenobserved that a relatively limited number of correction factor curvescan be used by establishing categories of battery types which tend torespond in the same manner. The exact number of curves can be varied toincrease the accuracy of the correction.

FIG. 8 is a graphical plot, similar to FIG. 4, illustratingstate-of-charge correction factor curves for five different types ofbatteries. These five battery types, ordered from the largest to thesmallest ratio of plate area to acid volume, are designated:

Acid Starved ("Deep Cycle")

Acid Limited ("Standard")

Acid Balanced

Acid Reserve

Acid Flooded ("Utility")

The five curves of FIG. 8 were each determined empirically fromexperimental data in the same manner as is described above withreference to the single "standard" curve of FIG. 4. Similar to theapproximation discussed above with reference to FIG. 5, each of thecorrection factor curves illustrated in FIG. 8 can be described usingsegmented piecewise-linear approximations for implementation by theelectronic testing devices of the present invention.

The invention provides for the use of one of the standard curvesillustrated in FIG. 8, or for the use of one of an infinite variety ofcurves, as is required to best represent the battery being tested.Theoretically, every battery type or style in existence can beaccurately correlated to a specific correction factor curve, so long asthe specific battery type can be identified by a stock number or byother identifying codes or designations.

In some embodiments of the present invention, in addition to acompensation factor curve being chosen which most closely represents thecharacteristic performance of the battery being tested, a thresholdvoltage for the battery being tested is also selected. Recall that thethreshold voltage is the open circuit voltage, for a particular batterytype, below which an indication should be given that the battery must becharged before testing can be continued. A wide variety of correctionfactor functions or look-up tables and threshold voltages can beprogrammed into a microprocessor in the testing equipment. Theparticular battery type (B) is identitied to the battery tester. Byutilizing the particular correction factor function and thresholdvoltage most closely correlated to the specific battery type beingtested, the "fully-charged" dynamic conductance can be more accuratelydetermined and a more accurate indication of the condition of thebattery can be given.

FIG. 9 discloses a simplified block diagram of another embodiment of animproved electronic battery testing/monitoring device with automaticcompensation for low state-of-charge. This embodiment eliminates thecorrection amplifier 36 and chopper switch 34 of the first embodimentdisclosed in block diagram form in FIG. 3. Instead, it contains amicroprocessor represented generally by block 220 of FIG. 9. Further,this embodiment allows the automatic state-of-charge compensation to betailored for the specific battery type. Microprocessor block 220includes all of the usual elements which comprise a microprocessorsystem such as the requisite logic elements, a clock oscillator, arandom access memory, a firmware program contained in read-only memory,and, of course, the processor itself. The memory and other componentscan be integrated with the microprocessor, or they can be distinctexternal components coupled the microprocessor for operation therewith.With the embodiment of FIG. 9, the appropriate correction for lowstate-of-charge is performed by microprocessor block 220 under thecontrol of the firmware program contained therein.

Microprocessor block 220 is programmed with functional representationsof multiple state-of-charge correction factor curves, such as thoseillustrated in FIG. 8, for a number of different battery types (B).Alternatively, microprocessor block 220 can be programmed with look-uptable data representative of multiple state-of-charge correction factorcurves. Further, voltage threshold values, below which the battery mustbe recharged prior to testing, are programmed into microprocessor block220. The voltage threshold values and the state-of-charge correctionfactor functions, curves, or look-up tables can be stored for example,in the ROM or RAM associated with microprocessor block 220.Alternatively, this data can be programmed into EEPROM type memorydevices. Further, this data can be updated or altered using a keyboard,a modem communication link with another system, and/or with any othertype of suitable input device.

Battery type information is provided to microprocessor block 220 atinput 300 using input device 301. Input device 301 can be a keypad entrydevice, a barcode reader, a menu driven terminal or any other type ofinput device adapted for supplying battery type information about thebattery being tested to microprocessor block 220. Battery type relatedinformation B can include battery manufacturer serial numbers, modelinformation, manufacturer data, battery ratings in cold cranking amps(CCA), vehicle identification numbers or any other information or formatwhich can be used to inform microprocessor block 220 of the particulartype, class, group or characteristics of the battery being tested. Withbattery type information provided to microprocessor block 220 at input300, microprocessor block 220 can tailor the state-of-charge correctionby selecting an appropriate correction factor function and thresholdvoltage which most closely correlate to the battery type of theparticular battery being tested.

A description of operation of most of the elements of FIG. 9 parallelsthe description of operation of the embodiment disclosed in FIG. 3.Signals representative of the signal at output 10 of high-gain amplifiercascade 12 are fed back to input 20 of high-gain amplifier cascade 12 bymeans of two feedback paths; internal feedback path 14 and externalfeedback path 16. Internal feedback path 14 includes low pass filter(LPF) 18 and feeds a signal voltage directly back to input 20 ofhigh-gain amplifier cascade 12. External feedback path 16 containsresistive network 22 and feeds a signal current back to the batteryundergoing test 24. Summation circuitry 26 combines the resulting signalvoltage 28 developed thereby across battery 24 with a periodicsquare-wave signal voltage 30.

In the embodiment of FIG. 9, signal voltage 30 simply comprises theconstant output signal of oscillator 32. The oscillation frequency ofoscillator 32 may, for example, be 100 Hz. This periodic signal voltageis presented to summation circuitry 26 along with the signal voltage 28developed across battery 24, the resulting composite signal voltage 44at the output of summation circuitry 26 is then capacitively coupled toinput 20 of high-gain amplifier cascade 12 by means of capacitivecoupling network 46. Accordingly, the voltage at output 10 of high-gainamplifier cascade 12 comprises a constant dc bias component along withan ac signal component that is proportional to the dynamic conductanceG_(x) of the battery undergoing test 24. The constant dc bias componentis ignored while the variable ac signal component is detected andaccurately converted to a dc signal voltage by synchronous detector 48,synchronized to the oscillator by means of synchronizing path 50.

The dc signal level at output 52 of synchronous detector 50 isproportional to the battery's dynamic conductance G_(x). This analogvoltage is converted to a corresponding digital representation of G_(x)by analog to digital (A/D) converter 222 and then inputted tomicroprocessor block 220 through input port 224. In addition, thebattery's unloaded voltage V_(o) is connected via dc path 38 to theinput of analog to digital converter 226. A corresponding digitalrepresentation of V_(o) at the output of A/D converter 226 is therebyinputted to microprocessor block 220 through input port 228.

By programmed algorithmic techniques that are well-known to thoseskilled in the art, the microprocessor's firmware program utilizes thedigital representation of V_(o) to correct the digital representation ofG_(x) for the battery's state-of-charge. This can be done, for example,by inputting V_(o) to a "look-up table" whose output is thecorresponding correction factor F, and then multiplying G_(x) by theresulting factor F to obtain the corrected conductance value, G_(x)(12.6). Alternatively, the appropriate value of G_(x) (12.6) could becalculated directly by numerically evaluating the reciprocal of theempirical relationship disclosed in Equation 1. In either case, inpreferred embodiments, the microprocessor uses the battery typeinformation from input device 301 provided at input 300 to tailor thestate-of-charge correction by selecting the appropriate correctionfactor function and threshold voltage which most closely correlate tothe battery type.

In order to emulate a quantitative-type electronic battery tester, anumerical value proportional to G_(x) (12.6) is outputted and displayedon a digital display such as 236 interfaced through output port 234, orprinted by a printer such as 240 interfaced to microprocessor 220through output port 238. In addition, whenever V_(o) is less than apredetermined minimum value determined as a function of the particulartype of battery being tested, the firmware program suppresses thenumerical display and instead provides an indication to the user thatthe battery must be recharged before testing. This special informationcan, for example, be displayed by digital display 236, printed byprinter 240, or conveyed to the user by an LED 66 interfaced tomicroprocessor 220 through output port 242.

For emulation of a qualitative ("pass/fail") electronic battery tester,the battery's rating is first inputted to microprocessor 220 through aninput device such as a shaft encoder 230 interfaced to microprocessor220 through input port 232. A dial associated with shaft encoder 230 iscalibrated in battery rating units such as cold cranking amperes orampere-hours. By programmed algorithmic techniques that are well-knownto those skilled in the art, the microprocessor's firmware program thendirects microprocessor block 220 to compare the dynamic conductancecorrected for state-of-charge, G_(x) (12.6), with a reference valueappropriate to the inputted battery rating and to output the resultingpass/fail information to the user. This qualitative output informationcan, for example, be displayed by digital display 236, printed byprinter 240, or conveyed to the user by an LED 246 interfaced tomicroprocessor 220 through output port 244. Again, if V_(o) is less thana predetermined minimum value, the displayed information is suppressedand the user is informed that the battery must be recharged beforetesting. This special information can, for example, be displayed bydigital display 236, printed by printer 240, or conveyed to the user byLED 66.

FIG. 10 discloses a simplified block diagram of another embodiment of animproved electronic battery testing/monitoring device with battery-typespecific automatic compensation for low state-of-charge. Like theembodiment disclosed in FIG. 9, this embodiment employs a microprocessorblock 220 to implement the appropriate correction for lowstate-of-charge. It differs from the embodiment of FIG. 9, however, inthat the hardware inputs a digital representation of the battery'sdynamic resistance R_(x) to microprocessor 220 which then utilizes itsfirmware program to calculate the reciprocal quantity, the battery'sdynamic conductance G_(x) =1/R_(x), as well as to correct for thebattery's state-of-charge.

The hardware disclosed in FIG. 10 functions as follows: Oscillator 32generates a periodic square-wave signal 42 which is inputted directly tocurrent amplifier 244. The oscillation frequency of oscillator 32 may,for example, be 100 Hz. The output of current amplifier 244, a periodicsignal current 246, then passes through battery 24. By virtue of thefact that the output resistance of current amplifier 244 is much largerthan the battery's dynamic resistance R_(x), the amplitude of signalcurrent 246 will be virtually independent of R_(x). Accordingly, theresultant ac signal voltage 248 appearing across the battery's terminalswill be directly proportional to the battery's dynamic resistance R_(x).Capacitive coupling network 250 couples the ac signal voltage 248 toinput 252 of voltage amplifier 254. This coupling network suppresses thebattery's dc terminal voltage but permits amplification of the ac signalvoltage by voltage amplifier 254. The output voltage 256 of voltageamplifier 254 provides the input to synchronous detector 48 which issynchronized to oscillator 32 by means of synchronizing path 50.Accordingly, a dc signal voltage 52 appears at the output of synchronousdetector 48 that is directly proportional to the battery's dynamicresistance R_(x).

The analog voltage 52 is converted to a corresponding digitalrepresentation of R_(x) by analog to digital (A/D) converter 222 andthen inputted to microprocessor block 220 through input port 224. Inaddition, the battery's unloaded voltage V_(o) is connected via dc path33 to the input of analog to digital converter 226. A correspondingdigital representation of V_(o) at the output of A/D converter 226 isthereupon inputted to microprocessor block 220 through input port 228.

As was the case with the battery tester of FIG. 9, battery-typeinformation is provided to the microprocessor at input 300 using inputdevice 301. Microprocessor block 220 then uses this information toselect one of a number of conversion functions or look-up tables to beused in the state-of-charge correction step. By programmed algorithmictechniques that are well-known to those skilled in the art, themicroprocessor's firmware program directs microprocessor block 220 toinvert the digital representation of R_(x) to obtain a digitalrepresentation of the battery's dynamic conductance G_(x). It thenutilizes the digital representation of V_(o) to correct the digitalrepresentation of G_(x) for the battery's state-of-charge. This can bedone, for example, by inputting V_(o) to a "look-up table" whose outputis the corresponding correction factor F, and then multiplying G_(x) bythe resulting factor F to obtain the corrected conductance value, G_(x)(12.6); or by computing G_(x) (12.6) directly from is the reciprocal ofthe empirical relationship disclosed in Equation 1. Alternatively, acorrected value of R_(x), R_(x) (12.6), can be computed first and thenalgorithmically inverted to obtain G_(x) (12.6).

In order to emulate a quantitative-type electronic battery tester, anumerical result proportional to G_(x) (12.6) is outputted and displayedon a digital display such as 236 interfaced through output port 234, orprinted by a printer such as 240 interfaced to microprocessor 220through output port 238. In addition, whenever V_(o) is less than apredetermined minimum value, preferably specific to the particular typeof battery being tested, the firmware program suppresses the numericaldisplay and instead provides an indication to the user that the batterymust be recharged before testing. This information can, for example, bedisplayed by digital display 236, printed by printer 240, or conveyed tothe user by an LED 66 interfaced to microprocessor 220 through outputport 242.

For emulation of a qualitative ("pass/fail") type of electronic batterytester, the battery's rating is inputted to microprocessor 220 throughan input device such as a shaft encoder 230 interfaced to microprocessor220 through input port 232. A dial associated with shaft encoder 230 iscalibrated in battery rating units such as cold cranking amperes orampere-hours. By programmed algorithmic techniques that are well-knownto those skilled in the art, the microprocessor's firmware programdirects microprocessor block 220 to compare the computed quantity, G_(x)(12.6), with a reference quantity appropriate to the inputted batteryrating to determine whether the battery passes or fails. For a computedquantity larger than the reference quantity, the battery passes.Otherwise it fails. Alternatively, a comparison can be made between thecomputed quantity R_(x) (12.6) and a corresponding reference quantityappropriate to the inputted battery rating to determine whether thebattery passes or fails. For a computed quantity less than the referencequantity, the battery passes. Otherwise it fails. In either case, thisqualitative information is outputted and displayed by digital display236, printed by printer 240, or conveyed to the user by an LED 246interfaced to microprocessor 220 through output port 244. Again, ifV_(o) is less than a predetermined minimum value, the display ofqualitative information is suppressed and the user is informed that thebattery must be recharged before testing. This special information can,for example, be displayed by digital display 236, printed by printer240, or conveyed to the riser by LED 66.

The improved electronic battery testing device of the present invention,as illustrated in FIGS. 9 and 10, can also be implemented using ananalog circuit such as the one illustrated in FIG. 3. FIG. 11 showsportions of one possible implementation of correction amplifier 36 fromthe electronic testing device illustrated in FIG. 3. As shown in FIG.11, correction amplifier 36 is, for ease of illustration, divided intosections 36A and 36B. The DC terminal or open circuit voltage V_(o) isapplied to section 36A of the correction amplifier at input 38.Analog-to-digital converter 310 of correction amplifier section 36Aconverts open circuit voltage V_(o) to a digitally represented value andprovides this digital value to microprocessor block 220 at input 315.Microprocessor block 220 of correction amplifier section 36B usesbattery type information obtained at input 300 from input device 301 toselect which of a variety of state-of-charge correction factor curves,functions or look-up tables best correlates to the particular type ofbattery being tested. Microprocessor block 220 then provides a digitalsignal at output 318 which is representative of a DC voltage, derivedfrom open circuit voltage V_(o) having a voltage level that is inverselyrelated to V_(o) --and hence is inversely related to the state-of-chargeof the battery being tested or monitored. Digital-to-analog converter320 then converts the derived voltage into analog signal 40. Portions36A and 36B of the correction amplifier illustrated in FIG. 11 can beused as correction amplifier 36 in the device shown in FIG. 3 to providebattery-type specific compensation.

Additionally, microprocessor block 220 shown in FIG. 11 can be used toform a variety of other functions. For example, chopper disable signal62 from correction amplifier 36 can also be provided as an output ofmicroprocessor block 220. Further, from FIG. 3, the output of DCmilliammeter 60 can be provided to analog-to digital converter 330 forconversion to a digital signal which is supplied at input 332 tomicroprocessor block 220. Thus, the output reading of DC milliammeter60, which is proportional to the corrected dynamic conductance of thebattery, can be provided to microprocessor 220. Hence, microprocessor220 can use this information to provide outputs 244, 234, 238 and or 242of the type shown in FIGS. 9 and 10. Thus, LEDs, displays and orprinters can be controlled by microprocessor block 220 to display theresults of the battery test.

Additionally, it is possible to implement the multiple state-of-chargecorrection factor curve approach of the present invention with limitedor no use of a microprocessor. For example, each of multiple correctionamplifiers 36 of the type illustrated in FIG. 6 can be separatelytailored for use with different battery types to implement acorresponding state-of-charge correction factor curve. Then, amicroprocessor, a manually controlled switch, or other control devicescan be used to switch the appropriate correction amplifier into thecircuit. In the alternative, a single correction amplifier of the typeillustrated in FIG. 6 can be used with selectable components to achievevarious piece-wise-linear curves, depending on the battery type beingtested.

Although three specific modes for carrying out the invention hereof havebeen described, it should be understood that many modifications andvariations can be made without departing from what is regarded to be thescope and subject matter of the invention. For example, the inventionmay comprise a single, self-contained, instrument that is temporarilyconnected to the battery to test the battery on-site. Alternatively, thedevice may comprise a monitoring device that is semi-permanentlyconnected to the battery to provide continuous monitoring of thebattery's condition at a remote location. In this latter case, thedevice will probably be separated into two parts--one part connected tothe battery and located at the battery's site; the other part containingthe remote display and located at the remote location. The divisionbetween the two parts can be made somewhat arbitrarily. Further, thedevice can measure either the dynamic conductance of a battery, or thedynamic resistance of the battery. Therefore, as used herein, the term"dynamic battery parameter" is intended to refer to either the dynamicconductance or the dynamic resistance of a battery. We contend that allsuch divisions, modifications, and variations fall within the scope ofthe invention disclosed herein and are therefore intended to be coveredby the appended claims.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An electronic device for monitoring or testing abattery having one of a plurality of battery types associated therewith,comprising:input circuitry for receiving information related to the typeof the battery; dynamic battery parameter determining circuitry fordetermining an intermediate dynamic parameter of the battery; opencircuit voltage sense circuitry coupled to the battery for sensing anopen circuit voltage of the battery; correction circuitry coupled to thedynamic battery parameter determining circuitry, to the open circuitvoltage sense circuitry and to the input circuitry which adjusts thedetermined intermediate dynamic parameter based upon the battery typeinformation and upon a value of the open circuit voltage of the battery;output circuitry coupled to the correction circuitry for providing testresults indicative of the condition of the battery, wherein the testresults are provided as a function of the adjusted intermediateparameter.
 2. The electronic device of claim 1 wherein the test resultscomprise qualitative results in conformance with the adjustedintermediate dynamic parameter relative to a reference dynamic parametervalue.
 3. The electronic device of claim 1 wherein the correctioncircuitry comprises a microprocessor and wherein digital representationsof the open circuit voltage and the intermediate dynamic parameter areboth inputted to the microprocessor and combined algorithmically toadjust the intermediate dynamic parameter.
 4. The electronic device ofclaim 1 wherein the output circuitry provides a special indication whenthe open circuit voltage is less than a predetermined value andsuppresses the test results when the open-circuit voltage is less thanthe predetermined value.
 5. The electronic device of claim 1 wherein thedynamic battery parameter determining circuitry comprises:a time varyingcurrent source coupled to the battery for providing a currenttherethrough; voltage response sense circuitry for sensing a responsevoltage between two terminals of the battery developed in response tothe current flowing therethrough; and detection circuitry coupled to thesense circuitry for determining the intermediate dynamic parameter ofthe battery based upon the current and the sensed response voltage. 6.The electronic device of claim 5 wherein the time varying current sourcecomprises a load.
 7. The electronic device of claim 1 wherein thedynamic battery parameter determining circuitry comprises:a time varyingvoltage source for applying a time varying voltage between two terminalsof the battery; current response sense circuitry for sensing a currentflowing through the battery developed in response to the time varyingvoltage applied thereto; detection circuitry coupled to the sensecircuitry for determining the intermediate dynamic parameter of thebattery based upon the time varying voltage and the sensed responsecurrent.
 8. The electronic device of claim 7 wherein the currentresponse sense circuitry senses current flowing through a load.
 9. Theelectronic device of claim 1 wherein the intermediate parameter of thebattery is a dynamic couductance of the battery, and wherein thecorrection circuitry adjusts the dynamic conductance in inversecorrespondence with the value of the open circuit voltage of thebattery.
 10. The electronic device of claim 9 wherein the test resultscomprise numbers proportional to the adjusted intermediate dynamicconductance.
 11. The electronic device of claim 1 wherein theintermediate dynamic parameter of the battery is a dynamic resistance ofthe battery, and wherein the correction circuitry adjusts the dynamicresistance in direct correspondence with the value of the open circuitvoltage of the battery.
 12. The electronic device of claim 11 whereinthe test results comprise numbers inversely proportional to the adjustedintermediate dynamic resistance.